5:15 PM - 7:15 PM
[SGD03-P17] Atmospheric loading and gravity change associated with the atmospheric waves due to the 2022 Tonga volcanic eruption
Keywords:continuous relative gravity observation, Tonga volcanic eruption, atmospheric pressure change, atmospheric loading, Lamb wave
The Hunga Tonga-Hunga Ha’apai volcano erupted at around 13:00 JST on January 15, 2022. Atmospheric waves were excited due to the eruption, and their propagation was observed as air pressure changes around the world. Imanishi (2022) analyzed the continuous gravity data collected by the superconducting gravimeter iGrav#028 at Matsushiro, and found the gravity change of ~0.5 microGal associated with the air pressure change due to the eruption. He also modeled the gravity change by applying the theory of acoustic-gravity wave (AGW) proposed in Zürn and Wielandt (2007), and showed that the inertial effect due to atmospheric loading was clearly detected. In the analysis, he applied the low-pass filter with a cutoff frequency of 2.5 mHz to the original gravity data, and he used the Lamé parameters lambda = mu = 40 GPa in the theoretical calculations.
Oda et al. (2025) analyzed the continuous gravity data collected by the LaCoste G031 gravimeter at Kyoto University, and found the gravity change of ~1.4 microGal (in the frequency bands of 0.1–10 mHz) associated with the air pressure change due to the eruption. They applied the band-pass filter with frequency bands of 0.1–1 mHz and 1–10 mHz to the original gravity data, and modeled each gravity change by applying the theory of AGW. The gravity changes can be explained by the AGW theory, if the elastic parameters at the depths of 30 and 10 km of the PREM (Dziewonski and Anderson, 1981) were used in calculating the theoretical gravity changes for the frequency bands of 0.1–1 mHz and 1–10 mHz, respectively. These results indicate that the gravity changes are sensitive to different depths corresponding to wavelength of the air pressure waves.
In the first place, the AGW theory used by Imanishi (2022) and Oda et al. (2025), consists of the three components, namely, Newtonian, free-air and inertial effects. The free-air and inertial effects result from the atmospheric loading. In the AGW theory, the vertical displacement associated with the air pressure change was calculated following Sorrells (1971), and the Lamé parameters exist only in the formula of Sorrells (1971). The formula of Sorrells (1971) is based on a homogeneous elastic half-space, but the elasticity of the Earth has a vertically heterogeneous structure, so the observed gravity change has some information about the vertically heterogeneous structure beneath the station.
Therefore, we calculated the vertical displacement associated with the air pressure change, by using the method of Tanimoto and Wang (2019), which allows model calculations to take account of the vertically heterogeneous structure, and using a structure constructed from the PREM. We also developed a modified AGW theory which allows model calculations to take account of the vertically heterogeneous structure, by replacing the formula of Sorrells (1971) with the numerically calculated displacement. We created a synthetic gravity waveform using the modified AGW theory, and found that the synthetic gravity change agrees with the observed gravity change of ~1.4 microGal (in the frequency bands of 0.1–10 mHz) at Kyoto University, without splitting the frequency band. The root-mean-square error is 0.09 microGal. Next, we analyzed the gravity changes of ~2.0 and ~2.6 microGal (in the frequency bands of 0.1–10 mHz) collected by the gPhone #163 gravimeter at Mt. Fuji and the superconducting gravimeter iGrav#003 at Mt. Zao, respectively. We found that the observed gravity changes can be explained by the modified AGW theory with 0.15 and 0.19 microGal root-mean-square error. These results indicate that the continuous relative gravity observations clearly detected the atmospheric loading associated with the propagation of the atmospheric waves due to the 2022 Tonga volcanic eruption, and the atmospheric loading has some information about the vertically heterogeneous structure beneath the station.
Oda et al. (2025) analyzed the continuous gravity data collected by the LaCoste G031 gravimeter at Kyoto University, and found the gravity change of ~1.4 microGal (in the frequency bands of 0.1–10 mHz) associated with the air pressure change due to the eruption. They applied the band-pass filter with frequency bands of 0.1–1 mHz and 1–10 mHz to the original gravity data, and modeled each gravity change by applying the theory of AGW. The gravity changes can be explained by the AGW theory, if the elastic parameters at the depths of 30 and 10 km of the PREM (Dziewonski and Anderson, 1981) were used in calculating the theoretical gravity changes for the frequency bands of 0.1–1 mHz and 1–10 mHz, respectively. These results indicate that the gravity changes are sensitive to different depths corresponding to wavelength of the air pressure waves.
In the first place, the AGW theory used by Imanishi (2022) and Oda et al. (2025), consists of the three components, namely, Newtonian, free-air and inertial effects. The free-air and inertial effects result from the atmospheric loading. In the AGW theory, the vertical displacement associated with the air pressure change was calculated following Sorrells (1971), and the Lamé parameters exist only in the formula of Sorrells (1971). The formula of Sorrells (1971) is based on a homogeneous elastic half-space, but the elasticity of the Earth has a vertically heterogeneous structure, so the observed gravity change has some information about the vertically heterogeneous structure beneath the station.
Therefore, we calculated the vertical displacement associated with the air pressure change, by using the method of Tanimoto and Wang (2019), which allows model calculations to take account of the vertically heterogeneous structure, and using a structure constructed from the PREM. We also developed a modified AGW theory which allows model calculations to take account of the vertically heterogeneous structure, by replacing the formula of Sorrells (1971) with the numerically calculated displacement. We created a synthetic gravity waveform using the modified AGW theory, and found that the synthetic gravity change agrees with the observed gravity change of ~1.4 microGal (in the frequency bands of 0.1–10 mHz) at Kyoto University, without splitting the frequency band. The root-mean-square error is 0.09 microGal. Next, we analyzed the gravity changes of ~2.0 and ~2.6 microGal (in the frequency bands of 0.1–10 mHz) collected by the gPhone #163 gravimeter at Mt. Fuji and the superconducting gravimeter iGrav#003 at Mt. Zao, respectively. We found that the observed gravity changes can be explained by the modified AGW theory with 0.15 and 0.19 microGal root-mean-square error. These results indicate that the continuous relative gravity observations clearly detected the atmospheric loading associated with the propagation of the atmospheric waves due to the 2022 Tonga volcanic eruption, and the atmospheric loading has some information about the vertically heterogeneous structure beneath the station.